Roughly 140 million people worldwide are chronically exposed to As-contaminated drinking water at concentrations exceeding the World Health Organization (WHO) standard of 10 µg/L. Arsenic is a class I carcinogen known to cause several types of cancer and ischemic heart disease. Metabolism of inorganic As (InAs), which facilitates urinary As excretion, relies on one-carbon metabolism and involves two methylation steps; both utilize S-adenosylmethionine (SAM) as the methyl donor. SAM biosynthesis relies on B vitamins including folate and B12 for the recruitment and transfer of methyl groups, but other nutrients, including choline and betaine, also contribute to the methyl pool. Our recent findings from a cross-sectional study of Bangladeshi adults exposed to a wide range of As concentrations in drinking water show that plasma choline and betaine concentrations are positively associated with As methylation. These findings suggest that choline and/or betaine may play an important role in As methylation and elimination and that simple interventions may have therapeutic potential for the many populations at risk for As-induced health effects.